FIELD OF THE INVENTION
The present invention relates to improved apparatus and method for forming grooves in the inner wall surface of metal pipes, tubing and the like. The apparatus for effecting the grooving is embodied in a floating plug of the type used in drawing tubes from a larger to a smaller diameter, with or without a corresponding reduction in wall thickness. The plug has external teeth means which extend axially along the plug and which are specially configured and dimensioned to define approach and bearing portions that, in cooperation with a surrounding die, effect plastic deformation of the inner tube wall into the desired grooved geometry. Depending upon the depth of groove desired (or corresponding rib height) one or more draws may be effected to achieve final dimensions. Generally, to obtain full groove depth, multiple draw passes are made, to increase the depth of the groove incrementally; this to preclude the drawing tension from exceeding the ultimate tensile strength of the tube and causing tube rupture.